Bi-directional fluid-structure interaction for prediction of tip clearance influence on a composite ducted propeller
Introduction
With the rapid development of composite materials throughout the world, the use of advanced materials has become very common in marine propellers. In the past, manganese-nickel-aluminum-bronze (MAB) or nickel-aluminum-bronze (NAB) were commonly used as the primary material for propeller construction in the maritime industry due to many reasons such as its superior corrosion resistance, high-yield strength, reliability, and affordability(Young et al., 2012). But these materials are heavy, expensive, and creates noise and vibration in complex propeller geometries. As an alternative, composite propellers take advantage of the outstanding material properties of composites such as lightweight, high strength-to-weight ratio, high stiffness-to-weight ratio, and greater geometrical design flexibility. Light composite materials can make the design of the blades thicker and more flexible to improve hydrodynamic performance. Moreover, composites can bring us the potential benefits of reduced corrosion and cavitation damage, improved fatigue performance, reduced noise, improved material damping properties, reduced manufacturing cost and lifetime maintenance cost (Motley et al., 2009; Motley and Young, 2011).
Ducted propellers are typical propulsion units widely used in the marine industry. It is composed of a propeller surrounded by an annular duct. Compared with the conventional propulsion propeller, ducted propellers are very useful by providing advanced operability and higher bollard thrust to support marine vessels (Funeno, 2017). It is used to improve the efficiency of the propeller and is especially used on heavily loaded propellers or propellers with limited diameter. A lot of experimental and theoretical research has been done on ducted propellers(Bontempo et al., 2015; Gaggero et al., 2012; Oosterveld, 1967, 1970; Thurston and Amsler, 1966).
The issue of tip clearance effect has been the subject of many studies on hydraulic machinery such as ducted propellers, pumps and turbines for years. Energy-saving and stable operating have become the primary factors for the study of the tip clearance effect. The existence of tip clearance has a significant influence on the efficiency of the machinery (Liu et al., 2018). Tip clearance effect mainly includes tip clearance size, blade-tip rounding (YANG et al., 2007) and blade tip thickening (Mei and Zhou, 2015). Several studies on the effect of tip clearance size on water pumps show that the efficiency decreases as the tip clearance increases (Liu et al., 2017; Saha and Soundranayagam, 1996; Soundranayagam and Saha, 1996), and the pressure fluctuation is intensified with the expansion of the gap (Goto, 1992; Mei and Zhou, 2015b). The energy loss (decrease of efficiency) and unstable operation (intensified pressure fluctuation) are mainly caused by the enhanced tip-leakage vortex with the increasing tip clearance size. As one of the special types of hydraulic machinery, ducted propellers usually work in incompressible fluid flow and different working conditions. Similar conclusions on the ducted propeller were introduced in recent years. The influence of the tip clearance of a rigid ducted propeller was investigated by the incompressible Navier-Stokes equations with a Multiple Reference Frame (MRF) method by (Yongle et al., 2015). Results show that the efficiency decreases as the tip clearance increases at lower advance coefficient, while it has a revised point at higher advance coefficient. A pump-jet propulsor with different tip clearance sizes was simulated based on the CFD method (Lu et al., 2018, 2016). The efficiency of the propulsor dropped sharply with the increase of the tip clearance size under both the cavitation and non-cavitation condition. The propulsion performance and pressure fluctuation of a pump-jet propulsor were analyzed with different tip clearance size (Yu et al., 2019). When the tip clearance increases, the thrust and propulsion efficiency can be reduced significantly which are mainly caused by the change of time-averaged pressure distributions on the rotor blade. While the influence of tip clearance effect for ducted propellers mentioned above is based on metal blades, the influence on the composite ducted propeller is underway.
The ability to accurately predict the hydrodynamic coefficients of a composite ducted propeller is very important for the calculation method. The Reynolds Average Navier-Stokes (RANS) method has been widely used for calculating the ducted propeller performance for years (Krasilnikov et al., 2007; Majdfar et al., 2017; Sanchez-Caja et al., 2000). In this method, the propeller is considered as a rigid body. However, under the hydrodynamic pressure, the composite propeller undergoes deformation progress, which will lead to performance change in both hydrodynamic and structural regimes. A one-way coupling method, which applied the hydrodynamic forces as the external loads on the rotor, was used for analyzing a single-blade sewage water pump by (Benra, 2006). This method involved only the hydrodynamic influence on the structure; the hydrodynamic performance change due to the deformation of the structure was ignored. A coupled boundary element method (BEM) and finite element method (FEM) approach were applied on the study of FSI of composite propellers by (Y. L. Young, 2008). A FSI method of an impeller pump using OpenFOAM was developed and validated by (Campbell and Paterson, 2011). A large deformation laminated composite propeller was simulated by bi-directional FSI using commercial solvers (Kumar and Wurm, 2015). Recently, the commercial software with fluid-structure interaction solver with a coupled CFD/FEM model is widely used to analyze the hydrodynamic and structural performance of composite propellers.
In this paper, the modeling and simulation using the bi-directional FSI method of the composite ducted propeller, using commercial solvers based on the MRF method, are performed and validated. Then, several structural finite element models of the composite ducted propeller blade with different layups of carbon fiber reinforced plastic (CFRP) are built and examined. The analysis is done to check the mechanical performance and modal properties of the propeller with different stacking sequences and ply angles so that the most suitable layup for the ducted propeller is found. Finally, the fluid-structure coupling simulation of the composite ducted propeller with different tip clearance is presented. The influence of tip clearance on hydrodynamic performance and structural properties of the composite ducted propeller is evaluated.
Section snippets
Numerical method
In this paper, the numerical simulations are carried out on a standard ducted propeller geometry, the model Ka4-70 propeller with a 19 A duct, which was presented by MARIN (Maritime Research Institute of the Netherland) (Oosterveld, 1970). As shown in Fig. 1, the ducted propeller consists of composite blades with metal hub and duct. The diameter of the ducted propeller is D = 240 mm. The pitch-diameter ratio is P/D = 1. The tip clearance of the standard ducted propeller is 1 mm, which is the
Verification and validation
Since the standard tip clearance is 1 mm in the experimental results published by MARIN (Maritime Research Institute of the Netherland) (Carlton, 2018), the verification and validation are carried out on the model of the ducted propeller with the tip clearance of 1 mm.
To evaluate the hydrodynamic performance of marine propellers, the following non-dimensional coefficients are considered: the advance coefficient , total thrust coefficient , duct thrust coefficient , torque coefficient ,
Selection of proper structure for the composite propeller
To get a proper structure of the ducted propeller blades, five different FEM models of the ducted propeller are analyzed by applying hydrodynamic pressure to the composite blade at the design working condition J = 0.6 when the tip clearance size is 1 mm.
The five different stacking sequences with symmetric laminates [0i/±θ]s are selected for the composite ducted propeller blades, as shown in Table 3. The subscript ‘i’ denotes the number of 0° layer, ‘s’ denotes symmetric laminates. The
Results and discussion
After what has been analyzed above, the [04/±30]s stacking sequence shows better mechanical properties for the ducted propeller blade than other stacking sequences. The following discussion is all based on the [04/±30]s stacking sequence applied to the composite ducted propeller. Both metal and composite material properties are listed previously in Table 1. The results are all calculated using the bi-directional FSI method with the same mesh and turbulence model for the fluid domain introduced
Conclusions
A ducted propeller is an important part of a propulsion system which can lead to the improvement of thrust efficiency. The tip clearance change of the ducted propeller has a significant influence on the propeller performance. Hence, the gap size between the propeller and the duct can not be ignored. A bi-directional FSI method is presented for analysis of a composite ducted propeller. The method is validated on a metal ducted propeller and is able to predict the hydrodynamic performance and
Acknowledgements
Supports from National Natural Science Foundation of China (Grant No. 51875466) and China Postdoctoral Science Foundation (Grant No. 2019T120941) are greatly acknowledged. Besides, the research work was also supported by the Fundamental Research Funds for the Central Universities (Grant No. 3102020HHZY030003).
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2022, Ocean EngineeringCitation Excerpt :Martio (Martio et al., 2017) studied the virtual mass and damping coefficients of both open and ducted propellers, which were determined using URANS computations based on CFD method. An (An et al., 2020) analyzed the influence of the tip clearance on a composite ducted propeller using the bi-directional fluid-structure interaction (FSI) method which is coupled by CFD method and finite element method(FEM). An acceptable layup for the composite blade is found using this method.